Lithographic apparatus and device manufacturing method

ABSTRACT

A method and apparatus for cleaning the inside of an immersion lithographic apparatus is disclosed. In particular, a liquid supply system of the lithographic apparatus may be used to introduce a cleaning fluid into a space between the projection system and the substrate table of the lithographic apparatus. Additionally or alternatively, a cleaning device may be provided on the substrate table and an ultrasonic emitter may be provided to create an ultrasonic cleaning liquid.

This application is a continuation of co-pending U.S. patent applicationSer. No. 13/242,401, filed Sep. 23, 2011, which is a continuation ofU.S. patent application Ser. No. 12/986,576, filed Jan. 7, 2011, nowU.S. Pat. No. 8,638,419, which is a continuation of U.S. patentapplication Ser. No. 11/656,560, filed Jan. 23, 2007, now U.S. Pat. No.8,115,899, which is a continuation of U.S. patent application Ser. No.11/015,767, filed Dec. 20, 2004, now U.S. Pat. No. 7,880,860, thecontents of each of the foregoing applications is incorporated herein inits entirety.

FIELD

The present invention relates to a lithographic apparatus and a devicemanufacturing method. In particular, the present invention relates to acleaning device for an immersion lithographic apparatus and a method ofcleaning the projection system and/or the substrate table of animmersion lithographic apparatus.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.comprising part of, one, or several dies) on a substrate (e.g. a siliconwafer). Transfer of the pattern is typically via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate. Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively patterned. Known lithographic apparatusinclude so-called steppers, in which each target portion is irradiatedby exposing an entire pattern onto the target portion at one time, andso-called scanners, in which each target portion is irradiated byscanning the pattern through a radiation beam in a given direction (the“scanning”-direction) while synchronously scanning the substrateparallel or anti-parallel to this direction. It is also possible totransfer the pattern from the patterning device to the substrate byimprinting the pattern onto the substrate.

It has been proposed to immerse the substrate in the lithographicprojection apparatus in a liquid having a relatively high refractiveindex, e.g. water, so as to fill a space between the final element ofthe projection system and the substrate. The point of this is to enableimaging of smaller features since the exposure radiation will have ashorter wavelength in the liquid. (The effect of the liquid may also beregarded as increasing the effective NA of the system and alsoincreasing the depth of focus.) Other immersion liquids have beenproposed, including water with solid particles (e.g. quartz) suspendedtherein.

However, submersing the substrate or substrate and substrate table in abath of liquid (see, for example, U.S. Pat. No. 4,509,852, herebyincorporated in its entirety by reference) means that there is a largebody of liquid that must be accelerated during a scanning exposure. Thisrequires additional or more powerful motors and turbulence in the liquidmay lead to undesirable and unpredictable effects.

One of the solutions proposed is for a liquid supply system to provideliquid on only a localized area of the substrate and in between thefinal element of the projection system and the substrate using a liquidsupply system (the substrate generally has a larger surface area thanthe final element of the projection system). One way which has beenproposed to arrange for this is disclosed in PCT patent application WO99/49504, hereby incorporated in its entirety by reference. Asillustrated in FIGS. 2 and 3, liquid is supplied by at least one inletIN onto the substrate, preferably along the direction of movement of thesubstrate relative to the final element, and is removed by at least oneoutlet OUT after having passed under the projection system. That is, asthe substrate is scanned beneath the element in a −X direction, liquidis supplied at the +X side of the element and taken up at the −X side.FIG. 2 shows the arrangement schematically in which liquid is suppliedvia inlet IN and is taken up on the other side of the element by outletOUT which is connected to a low pressure source. In the illustration ofFIG. 2 the liquid is supplied along the direction of movement of thesubstrate relative to the final element, though this does not need to bethe case. Various orientations and numbers of in- and out-letspositioned around the final element are possible, one example isillustrated in FIG. 3 in which four sets of an inlet with an outlet oneither side are provided in a regular pattern around the final element.

Ideally, the projection system of a lithographic apparatus would neverneed to be cleaned, since this is a complicated and delicate task thatmay require lithographic apparatus downtime and dismantling of thelithographic apparatus. However, due to, for example, a liquid providedto a space between a final element of the projection system and asubstrate in an immersion lithographic apparatus, the final element maybecome contaminated as a result of chemical reactions or drying stains.Additionally or alternatively, a substrate table of the lithographicapparatus may become contaminated, particularly the area outside wherethe substrate is held on the substrate table.

Cleaning the projection system and/or the substrate table may be donemanually by a person wiping the projection system and/or substrate tablewith a soft tissue and using a mild solvent. As well as the downtimeproblem, this method may run the risk of scratching parts of thelithographic apparatus, such as the final element of the projection, anduneven cleaning that can create, for example, undesirable illuminationdose variations over the projection field when the final element iscleaned.

SUMMARY

Accordingly, it would be advantageous, for example, to provide a methodfor cleaning a final element of the projection system and/or a substratetable without having to dismantle the liquid supply system and/or whichdoes not run the risk of scratching.

According to an aspect of the present invention, there is provided alithographic apparatus, comprising:

a substrate table configured to hold a substrate;

a projection system configured to project a patterned beam of radiationonto the substrate, the projection system comprising a final opticalelement adjacent the substrate;

a liquid supply system configured to provide a liquid to a space betweenthe projection system and the substrate table; and

a cleaning device configured to clean the final optical element, thesubstrate table, or both.

According to another aspect of the invention, there is provided alithographic apparatus, comprising:

a substrate table configured to hold a substrate;

a projection system configured to project a patterned beam of radiationonto the substrate, the projection system comprising a final opticalelement adjacent the substrate;

a liquid supply system configured to provide a liquid to a space betweenthe projection system and the substrate table; and

a coater configured to coat the final optical element, the substratetable, or both.

According to another aspect of the invention, there is provided the useof a fluid supply system in a lithographic apparatus for the in-lineapplication of (i) a cleaning fluid, (ii) a coating fluid, (iii) acoating remover, or (iv) any combination of (i)-(iii), to a spacebetween a projection system and a substrate table of the lithographicapparatus.

According to another aspect of the invention, there is provided a sprayunit configured to spray a cleaning fluid onto a final optical elementof a lithographic apparatus projection system.

According to another aspect of the invention, there is provided anultrasonic emitter configured to turn a liquid confined in a spacebetween a projection system and a substrate table of lithographicapparatus into an ultrasonic cleaning liquid.

According to another aspect of the invention, there is provided a methodof cleaning a projection system optical element, a substrate table, orboth, in a lithographic apparatus configured to have a liquid in a spacebetween the optical element and the substrate table, the methodcomprising circulating a cleaning fluid through the space.

According to another aspect of the invention, there is provided a methodof coating a projection system optical element, a substrate table, orboth, in a lithographic apparatus configured to have a liquid in a spacebetween the optical element and the substrate table, the methodcomprising circulating a coating fluid through the space.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIGS. 2 and 3 depict a liquid supply system for use in a lithographicprojection apparatus;

FIG. 4 depicts another liquid supply system for use in a lithographicprojection apparatus;

FIG. 5 depicts a liquid supply system according to an embodiment of thepresent invention;

FIG. 6 depicts the liquid confinement structure of FIG. 5 positionedover the substrate table;

FIG. 7 depicts a wash station in the substrate table according to anembodiment of the invention; and

FIG. 8 depicts an ultrasonic cleaning bath according to an embodiment ofthe invention.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to oneembodiment of the invention. The apparatus comprises:

-   an illumination system (illuminator) IL configured to condition a    radiation beam B (e.g. UV radiation or DUV radiation).-   a support structure (e.g. a mask table) MT constructed to support a    patterning device (e.g. a mask) MA and connected to a first    positioner PM configured to accurately position the patterning    device in accordance with certain parameters;-   a substrate table (e.g. a wafer table) WT constructed to hold a    substrate (e.g. a resist-coated wafer) W and connected to a second    positioner PW configured to accurately position the substrate in    accordance with certain parameters; and-   a projection system (e.g. a refractive projection lens system) PS    configured to project a pattern imparted to the radiation beam B by    patterning device MA onto a target portion C (e.g. comprising one or    more dies) of the substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The support structure supports, i.e. bears the weight of, the patterningdevice, It holds the patterning device in a manner that depends on theorientation of the patterning device, the design of the lithographicapparatus, and other conditions, such as for example whether or not thepatterning device is held in a vacuum environment. The support structurecan use mechanical, vacuum, electrostatic or other clamping techniquesto hold the patterning device. The support structure may be a frame or atable, for example, which may be fixed or movable as required. Thesupport structure may ensure that the patterning device is at a desiredposition, for example with respect to the projection system. Any use ofthe terms “reticle” or “mask” herein may be considered synonymous withthe more general term “patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device being created in the targetportion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam which is reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above, or employing a reflective mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more support structures). In such“multiple stage” machines the additional tables may be used in parallel,or preparatory steps may be carried out on one or more tables while oneor more other tables are being used for exposure.

Referring to FIG. 1, the illuminator IL receives a radiation beam from aradiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDcomprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source may be an integral part of thelithographic apparatus, for example when the source is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD if required, may be referred to as a radiation system.

The illuminator IL may comprise an adjuster AD for adjusting the angularintensity distribution of the radiation beam. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, the illuminator IL maycomprise various other components, such as an integrator IN and acondenser CO. The illuminator may be used to condition the radiationbeam, to have a desired uniformity and intensity distribution in itscross-section.

The radiation beam B is incident on the patterning device (e.g., maskMA), which is held on the support structure MT (e.g., mask table), andis patterned by the patterning device. Having traversed the patterningdevice MA, the radiation beam B passes through the projection system PS,which focuses the beam onto a target portion C of the substrate W. Withthe aid of the second positioner PW and position sensor IF (e.g. aninterferometric device, linear encoder or capacitive sensor), thesubstrate table WT can be moved accurately, e.g. so as to positiondifferent target portions C in the path of the radiation beam B.Similarly, the first positioner PM and another position sensor (which isnot explicitly depicted in FIG. 1) can be used to accurately positionthe patterning device MA with respect to the path of the radiation beamB, e.g. after mechanical retrieval from a mask library, or during ascan. In general, movement of the support structure MT may be realizedwith the aid of a long-stroke module (coarse positioning) and ashort-stroke module (fine positioning), which form part of the firstpositioner PM. Similarly, movement of the substrate table WT may berealized using a long-stroke module and a short-stroke module, whichform part of the second positioner PW. In the case of a stepper (asopposed to a scanner) the support structure MT may be connected to ashort-stroke actuator only, or may be fixed. Patterning device MA andsubstrate W may be aligned using patterning device alignment marks M1,M2 and substrate alignment marks P1, P2. Although the substratealignment marks as illustrated occupy dedicated target portions, theymay be located in spaces between target portions (these are known asscribe-lane alignment marks). Similarly, in situations in which morethan one die is provided on the patterning device MA, the patterningdevice alignment marks may be located between the dies.

The depicted apparatus could be used in at least one of the followingmodes:

1. In step mode, the support structure MT and the substrate table WT arekept essentially stationary, while an entire pattern imparted to theradiation beam is projected onto a target portion C at one time (i.e. asingle static exposure). The substrate table WT is then shifted in the Xand/or Y direction so that a different target portion C can be exposed.In step mode, the maximum size of the exposure field limits the size ofthe target portion C imaged in a single static exposure.

2. In scan mode, the support structure MT and the substrate table WT arescanned synchronously while a pattern imparted to the radiation beam isprojected onto a target portion C (i.e. a single dynamic exposure). Thevelocity and direction of the substrate table WT relative to the supportstructure MT may be determined by the (de-)magnification and imagereversal characteristics of the projection system PS. In scan mode, themaximum size of the exposure field limits the width (in the non-scanningdirection) of the target portion in a single dynamic exposure, whereasthe length of the scanning motion determines the height (in the scanningdirection) of the target portion.

3. In another mode, the support structure MT is kept essentiallystationary holding a programmable patterning device, and the substratetable WT is moved or scanned while a pattern imparted to the radiationbeam is projected onto a target portion C. In this mode, generally apulsed radiation source is employed and the programmable patterningdevice is updated as required after each movement of the substrate tableWT or in between successive radiation pulses during a scan. This mode ofoperation can be readily applied to maskless lithography that utilizesprogrammable patterning device, such as a programmable mirror array of atype as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

A further immersion lithography solution with a localized liquid supplysystem is shown in FIG. 4. Liquid is supplied by two groove inlets IN oneither side of the projection system PL and is removed by a plurality ofdiscrete outlets OUT arranged radially outwardly of the inlets IN. Theinlets IN and OUT can be arranged in a plate with a hole in its centerand through which the projection beam is projected. Liquid is suppliedby one groove inlet IN on one side of the projection system PL andremoved by a plurality of discrete outlets OUT on the other side of theprojection system PL, causing a flow of a thin film of liquid betweenthe projection system PL and the substrate W. The choice of whichcombination of inlet IN and outlets OUT to use can depend on thedirection of movement of the substrate W (the other combination of inletIN and outlets OUT being inactive).

Another immersion lithography solution with a localized liquid supplysystem solution which has been proposed is to provide the liquid supplysystem with a liquid confinement structure which extends along at leasta part of a boundary of the space between the final element of theprojection system and the substrate table. The liquid confinementstructure is substantially stationary relative to the projection systemin the XY plane though there may be some relative movement in the Zdirection (in the direction of the optical axis). A seal is formedbetween the liquid confinement structure and the surface of thesubstrate. In an embodiment, the seal is a contactless seal such as agas seal. Such a system with a gas seal is disclosed in U.S. patentapplication Ser. No. 10/705,783, hereby incorporated in its entirety byreference.

FIG. 5 shows a liquid supply system comprising a liquid confinementstructure (sometimes referred to as an immersion hood or showerhead)according to an embodiment of the invention. In particular, FIG. 5depicts an arrangement of a reservoir 10, which forms a contactless sealto the substrate around the image field of the projection system so thatliquid is confined to fill a space between the substrate surface and thefinal element of the projection system. A liquid confinement structure12 positioned below and surrounding the final element of the projectionsystem PL forms the reservoir, Liquid is brought into the space belowthe projection system and within the liquid confinement structure 12.The liquid confinement structure 12 extends a little above the finalelement of the projection system and the liquid level rises above thefinal element so that a buffer of liquid is provided. The liquidconfinement structure 12 has an inner periphery that at the upper endpreferably closely conforms to the shape of the projection system or thefinal element thereof and may, e.g., be round. At the bottom, the innerperiphery closely conforms to the shape of the image field, e.g.,rectangular though this need not be the case.

The liquid is confined in the reservoir by a gas seal 16 between thebottom of the liquid confinement structure 12 and the surface of thesubstrate W. The gas seal is formed by gas, e.g. air, synthetic air, N₂or an inert gas, provided under pressure via inlet 15 to the gap betweenliquid confinement structure 12 and substrate and extracted via outlet14. The overpressure on the gas inlet 15, vacuum level on the outlet 14and geometry of the gap are arranged so that there is a high-velocitygas flow inwards that confines the liquid. It will be understood by theperson skilled in the art that other types of seal could be used tocontain the liquid such as simply an outlet to remove liquid and/or gas.

Referring to FIG. 5, the liquid confinement structure 12 and theprojection system PL are positioned in such a way over the substrate Wthat the substrate may be exposed, the patterned beam of radiationpassing through the liquid 11 from the projection system PL to thesubstrate W.

In FIG. 6, the liquid confinement structure 12 and the substrate tableWT have moved relative to each other so that the aperture holding liquidof the liquid confinement structure 12 is no longer completely over thesubstrate W. While the liquid confinement structure aperture extendsbeyond the surface of the substrate W, for example, the immersion liquid11 can be replaced with a cleaning fluid 110 which may be supplied tothe liquid confinement structure via the same outlet 13 as the immersionliquid 11. In this case, the cleaning device is the liquid confinementstructure.

The cleaning fluid 110 may be used to remove contaminants from both thefinal element of the projection system PL and/or the substrate table WT.Furthermore, the pressurized gas flow via outlet 14 and inlet 15 mayalso be used to clean the substrate table. Contaminants are washed awayor broken down and removed when the cleaning fluid 110 is removed andreplaced by immersion liquid 11, ready to expose the next substrate. Thecleaning fluid 110, which may be supplied by the liquid confinementstructure, itself may be a solvent, a detergent, a liquefied gas such ascarbon dioxide, or a dissolved gas such as oxygen, ozone or nitrogen.

The liquid confinement structure may be used to contain cleaning gasesas well as liquids. The gap between the projection system PL and theliquid confinement structure 12 may be temporarily closed during thecleaning action and even gases that are potentially harmful to humans orto other parts of the lithographic apparatus may be used.

This reduction in particle contamination by a different use of theliquid confinement structure may be beneficial for the processingquality of the lithographic apparatus. The cleaning action using theliquid confinement structure may be part of an exposure, or it may bepart of a maintenance action when, for example, contamination levelsrequire it. An advantage of this approach is that there is no need todismantle the lithographic apparatus to clean.

Software may be used to guide movement of the substrate table further inevery direction or desired direction than is required for mere exposureof the substrate. In this way, the entirety or a desired part of thesubstrate table WT may be cleaned because the entire or desired surfacemay, at some point, be beneath the liquid confinement structure.

Another cleaning device configured to supply cleaning fluid to theliquid confinement structure is, referring to FIG. 7, a cleaning station20 provided in the substrate table WT. When cleaning of the finalelement of the projection system PL and/or of the substrate table WT isrequired, the cleaning station 20 is moved relative to the liquidconfinement structure so that the cleaning station is below the finalelement. In this way, cleaning liquid 110 is provided from the cleaningstation 20 by a sprayer configured to sprayed the cleaning liquid 110into the reservoir of the liquid confinement structure 12 and onto thefinal element of the projection system PL. The cleaning liquid 110 canthereby clean the final element. Additionally or alternatively, thecleaning liquid 110 may fill up the reservoir so that the substratetable WT may be cleaned. Once cleaning is finished, the liquidconfinement structure 12 may then be activated so that ultra pure wateror any other appropriate liquid rinses away any remaining cleaningliquid. Instead of a cleaning liquid, the cleaning station may provide acleaning gas such as ozone or a plasma. In an embodiment, the cleaningliquid may be liquid CO₂ (this cleaning may be known as “snowcleaning”).

The cleaning fluid used will depend on the contaminant to be removed.Drying stains are usually salt deposits and depending on the exact salt,high or low pH solutions may be used. Other detergents may be used toremove metal deposits. For organic contaminants, organic solvents suchas heptane, hexane (which are non polar), alcohol, e.g. ethanol, oracetone (which are polar) may be used.

Further, a projection beam may be projected through the final element PLduring cleaning to break down certain organic contaminants.

In an embodiment, it is desired to avoid any mechanical contact with thefinal element to reduce the risk of scratching the final element.However, if it is needed, the liquid confinement structure 12 and/or thesubstrate table WT may contain a brush on a motor.

The cleaning station 20 may be positioned anywhere in or on thesubstrate table WT or in or on the liquid confinement structure 12 sothat the liquid confinement structure itself, a closing plate and so onmay also be cleaned. Many surfaces in an immersion lithographicapparatus are at risk of contamination because of drying stains,organics contaminants from the resist evaporating off the substrate,contaminations from the immersion liquid itself, and so on. Accordingly,the cleaning fluid 110, whether provided by the liquid confinementstructure 12 or by the cleaning station 20, may be provided to all thesame surfaces that may be exposed to immersion liquid.

FIG. 8 shows another embodiment in which the immersion system, and inparticular the final element of the projection system PL, may becleaned. In this case, rather than or as well as introducing a cleaningfluid 110, the liquid in the liquid confinement structure 12 may betransformed into an ultrasonic cleaning bath by the incorporation of anultrasonic emitter 30 in the substrate table WT and/or in the liquidconfinement structure 12 as a cleaning device.

Ultrasonic cleaning is particularly good for removing contaminants thathave dried and hardened, for example, salts on the final element of theprojection system PL. Ultrasonic cleaning is also useful for cleaning inareas that brushes or tissues cannot reach, such as the pimples in apimple or burl-plate of the substrate table WT.

As well as or instead of a cleaning fluid 110, a coating may beintroduced into the reservoir of the liquid confinement structure 12 viathe liquid confinement structure 12 and/or via the cleaning station 20.In this case, the liquid confinement structure and/or the cleaningstation may be referred to as a coater. The coating may be used toprotect the liquid confinement structure, the final element, or othersurfaces, or may be for other uses which would be clear to the personskilled in the art. A coating removal agent may be introduced into theliquid confinement structure in the same way.

Another cleaning device that may be used for cleaning microbiologicalcontamination (i.e., bacterial cultures) is UV radiation. The radiationsource of the lithographic apparatus may be used to supply this UVradiation, although another source could be used. For example, theradiation source of a lithographic apparatus may emit 193 nm radiation,a type of radiation which kills bacteria that may be present in theliquid confinement structure, on the substrate table, and/or on thefinal element.

There are at least two ways in which the UV radiation from theprojection system PL itself may be used to kill bacteria on thesubstrate table. A first way is with a closing plate that is transparentto the UV radiation so that the closing plate holds the liquid withinthe liquid confinement structure 12 but the UV radiation may nonethelessreach the substrate table WT and kill the bacteria on it. A second wayis not to use a closing disc, but to irradiate bacteria andsimultaneously to wash the dead bacteria away with the flow of theliquid in the liquid confinement structure 12.

In the case where bacteria is to be removed from the final element ofthe projection system PL or a surface of the liquid confinementstructure 12, the UV radiation may be provided by the projection systemPL itself as described above, or it may be provided by a separateoptical element. For example, an optical element positioned in the sameplace as the ultrasound emitter 30 in FIG. 8 may be used to supply theUV radiation to the final element of the projection system PL and/or asurface of the liquid confinement structure 12. The UV radiation may inthat case, for example, enter the liquid confinement structure 12 via aclosing plate that is transparent to the UV radiation.

Using UV radiation has an advantage of keeping microbiologicalcontamination low while preventing prolonged downtime, which can becaused by having to perform wet chemical sanitizing using hydrogenperoxide or ozonated water, for instance. This treatment can be carriedout as a preventative or curative measure.

In an embodiment, there is provided a lithographic apparatus,comprising: a substrate table configured to hold a substrate; aprojection system configured to project a patterned beam of radiationonto the substrate, the projection system comprising a final opticalelement adjacent the substrate; a liquid supply system configured toprovide a liquid to a space between the projection system and thesubstrate table; and a cleaning device configured to clean the finaloptical element, the substrate table, or both.

In an embodiment, the cleaning device comprises a liquid confinementstructure of the liquid supply system, the cleaning device configured toclean the final optical element in-line in the lithographic apparatus.In an embodiment, the cleaning device comprises an ultrasonictransmitter configured to turn liquid in the space into an ultrasoniccleaning liquid. In an embodiment, the cleaning device comprises anoptical element configured to supply low wavelength ultravioletradiation. In an embodiment, the liquid supply system comprises asurface that is transparent to the low wavelength ultraviolet radiation.In an embodiment, the low wavelength ultraviolet radiation has awavelength of about 193 nm. In an embodiment, the cleaning device isconfigured to supply a cleaning fluid to the space. In an embodiment,the cleaning fluid comprises a solvent. In an embodiment, the cleaningfluid comprise a detergent. In an embodiment, the cleaning fluidcomprises a dissolved gas. In an embodiment, the gas is selected fromoxygen, ozone or nitrogen. In an embodiment, the cleaning device is inthe substrate table. In an embodiment, the cleaning device comprises aspray unit. In an embodiment, the spray unit is configured to spray acleaning fluid onto the optical element, the substrate table, or both.In an embodiment, the cleaning fluid comprises ozone. In an embodiment,the cleaning fluid comprises plasma. In an embodiment, the cleaningfluid comprises liquid carbon dioxide. In an embodiment, the cleaningfluid comprises a non-polar organic solvent. In an embodiment, thecleaning fluid comprises a polar organic solvent. In an embodiment, thecleaning device is configured to clean only the final optical element orto clean only the substrate table.

In an embodiment, there is provided a lithographic apparatus,comprising: a substrate table configured to hold a substrate; aprojection system configured to project a patterned beam of radiationonto the substrate, the projection system comprising a final opticalelement adjacent the substrate; a liquid supply system configured toprovide a liquid to a space between the projection system and thesubstrate table; and a coater configured to coat the final opticalelement, the substrate table, or both.

In an embodiment, the coater comprises a spray unit in the substratetable. In an embodiment, the coater comprises a liquid confinementstructure of the liquid supply system, the coating device configured tocoat the final optical element in-line in the lithographic apparatus. Inan embodiment, the coating device is configured to coat only the finaloptical element or to clean only the substrate table.

In an embodiment, there is provided the use of a fluid supply system ina lithographic apparatus for the in-line application of (i) a cleaningfluid, (ii) a coating fluid, (iii) a coating remover, or (iv) anycombination of (i)-(iii), to a space between a projection system and asubstrate table of the lithographic apparatus.

In an embodiment, there is provided a spray unit configured to spray acleaning fluid onto a final optical element of a lithographic apparatusprojection system.

In an embodiment, there is provided an ultrasonic emitter configured toturn a liquid confined in a space between a projection system and asubstrate table of lithographic apparatus into an ultrasonic cleaningliquid.

In an embodiment, there is provided a method of cleaning a projectionsystem optical element, a substrate table, or both, in a lithographicapparatus configured to have a liquid in a space between the opticalelement and the substrate table, the method comprising circulating acleaning fluid through the space.

In an embodiment, there is provided a method of coating a projectionsystem optical element, a substrate table, or both, in a lithographicapparatus configured to have a liquid in a space between the opticalelement and the substrate table, the method comprising circulating acoating fluid through the space.

In European Patent Application No. 03257072.3, the idea of a twin ordual stage immersion lithography apparatus is disclosed. Such anapparatus is provided with two tables for supporting a substrate.Leveling measurements are carried out with a table at a first position,without immersion liquid, and exposure is carried out with a table at asecond position, where immersion liquid is present. Alternatively, theapparatus has only one table.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion”, respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of or about 365, 248, 193, 157 or 126 nm).

The term “lens”, where the context allows, may refer to any one orcombination of various types of optical components, including refractiveand reflective optical components.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. For example, the invention may take the form of acomputer program containing one or more sequences of machine-readableinstructions describing a method as disclosed above, or a data storagemedium (e.g. semiconductor memory, magnetic or optical disk) having sucha computer program stored therein.

One or more embodiments of the present invention may be applied to anyimmersion lithography apparatus, such as those types mentioned above,and whether the immersion liquid is provided in the form of a bath oronly on a localized surface area of the substrate. A liquid supplysystem is any mechanism that provides a liquid to a space between theprojection system and the substrate and/or substrate table. It maycomprise any combination of one or more structures, one or more liquidinlets, one or more gas inlets, one or more gas outlets, and/or one ormore liquid outlets, the combination providing and confining the liquidto the space. In an embodiment, a surface of the space may be limited toa portion of the substrate and/or substrate table, a surface of thespace may completely cover a surface of the substrate and/or substratetable, or the space may envelop the substrate and/or substrate table.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

1. A lithographic apparatus, comprising: a substrate table configured tohold a substrate; a projection system configured to project a patternedbeam of radiation onto the substrate, the projection system comprising afinal optical element adjacent the substrate; a liquid supply systemconfigured to provide a liquid to a space between the projection systemand the substrate table; and a cleaning device configured to clean thefinal optical element, the substrate table, or both.
 2. The apparatusaccording to claim 1, wherein the cleaning device comprises a liquidconfinement structure of the liquid supply system, the cleaning deviceconfigured to clean the final optical element in-line in thelithographic apparatus.
 3. The apparatus according to claim 1, whereinthe cleaning device comprises an ultrasonic transmitter configured toturn liquid in the space into an ultrasonic cleaning liquid.
 4. Theapparatus according to claim 1, wherein the cleaning device comprises anoptical element configured to supply low wavelength ultravioletradiation.
 5. The apparatus according to claim 4, wherein the liquidsupply system comprises a surface that is transparent to the lowwavelength ultraviolet radiation.
 6. The apparatus according to claim 4,wherein the low wavelength ultraviolet radiation has a wavelength ofabout 193 nm.
 7. The apparatus according to claim 1, wherein thecleaning device is configured to supply a cleaning fluid to the space.8. The apparatus according to claim 7, wherein the cleaning fluidcomprises a solvent.
 9. The apparatus according to claim 7, wherein thecleaning fluid comprise a detergent.
 10. The apparatus according toclaim 7, wherein the cleaning fluid comprises a dissolved gas.
 11. Theapparatus according to claim 10, wherein the gas is selected fromoxygen, ozone or nitrogen.
 12. The apparatus according to claim 1,wherein the cleaning device is in the substrate table.
 13. The apparatusaccording to claim 12, wherein the cleaning device comprises a sprayunit.
 14. The apparatus according to claim 13, wherein the spray unit isconfigured to spray a cleaning fluid onto the optical element, thesubstrate table, or both.
 15. The apparatus according to claim 14,wherein the cleaning fluid comprises ozone.
 16. The apparatus accordingto claim 14, wherein the cleaning fluid comprises plasma.
 17. Theapparatus according to claim 14, wherein the cleaning fluid comprisesliquid carbon dioxide.
 18. The apparatus according to claim 14, whereinthe cleaning fluid comprises a non-polar organic solvent.
 19. Theapparatus according to claim 14, wherein the cleaning fluid comprises apolar organic solvent.
 20. The apparatus according to claim 14, whereinthe cleaning device is configured to clean only the final opticalelement or to clean only the substrate table.